Relative pitch perception is the identification of the relationship between two successive pitches without identifying the pitches themselves. Absolute pitch perception is the identification of the pitch of a single note without relating it to another note. To date, most pitch algorithms have concentrated on detecting the absolute pitch of a signal. This paper presents an approach for relative pitch detection, and applies this approach to the problem of detecting the musical interval between two acoustic events. The approach is presented as it applies to the western system of music.